1. Field of the Invention
The present invention relates to a vibratory flow meter and method, and more particularly, to a vibratory flow meter and method for determining a fluid temperature of a flow material.
2. Statement of the Problem
Vibrating conduit sensors, such as Coriolis mass flow meters and vibrating densitometers, typically operate by detecting motion of a vibrating conduit that contains a flowing material. Properties associated with the material in the conduit, such as mass flow, density and the like, can be determined by processing measurement signals received from motion transducers associated with the conduit. The vibration modes of the vibrating material-filled system generally are affected by the combined mass, stiffness and damping characteristics of the containing conduit and the material contained therein.
A typical Coriolis mass flow meter includes one or more conduits that are connected inline in a pipeline or other transport system and convey material, e.g., fluids, slurries and the like, in the system. Each conduit may be viewed as having a set of natural vibration modes, including for example, simple bending, torsional, radial, and coupled modes. In a typical Coriolis mass flow measurement application, a conduit is excited in one or more vibration modes as a material flows through the conduit, and motion of the conduit is measured at points spaced along the conduit. Excitation is typically provided by an actuator, e.g., an electromechanical device, such as a voice coil-type driver, that perturbs the conduit in a periodic fashion. Mass flow rate may be determined by measuring time delay or phase differences between motions at the transducer locations. Two such transducers (or pickoff sensors) are typically employed in order to measure a vibrational response of the flow conduit or conduits, and are typically located at positions upstream and downstream of the actuator. The two pickoff sensors are connected to electronic instrumentation by cabling, such as by two independent pairs of wires. The instrumentation receives signals from the two pickoff sensors and processes the signals in order to derive a mass flow rate measurement.
Vibratory flow meters, such as Coriolis meters and vibratory densitometers, measure mass flow and density through the influence that these fluid properties have on a vibrating flow conduit or flow conduits. However, flow conduit vibration is also influenced by other variables, and the influence of these variables must be compensated for in the meter.
One variable that is known to affect measurement accuracy is temperature. Temperature affects the material and dimensional properties of the flow conduit (or conduits). As a result, the temperature of the flow material impacts the fluid vibration. In addition, the meter will achieve the temperature of the flow material over time, wherein the operational properties will change with the change in temperature.
The temperature of interest is the temperature of the vibrating flow conduit. However, for fluids with high heat capacity, this temperature is for all practical purposes equal to the fluid temperature.
The measurement of the temperature of the flow sensor is not a trivial task. One issue is the mounting of a temperature sensor. Poor temperature sensor mounting lowers the heat transfer through the meter and results in temperature measurement errors. Another issue is whether a meter temperature accurately reflects the temperature of the flow material. Depending on the heat transfer capability of the meter, the ambient temperature, and a temperature difference between the flow material and the meter, for example, the meter temperature will lag the actual temperature of the flow material. In addition, coating of the inside of the flow meter will affect the heat transfer properties.